This invention is concerned with a method of providing conductive tracks on a printed circuit and an apparatus suitable for use in carrying out the method.
A well known and convenient way of producing printed circuits includes the printing of electrically conductive tracks on a substrate, for example, using screen printing techniques. The tracks are printed using an electrically conductive ink which typically comprises a polymeric material having electrically conductive particles, for example, copper, silver or other suitable metal, dispersed in the polymeric composition. The polymeric materials are typically cured to a solid condition by subjecting them to radiation, for example, infra-red radiation or ultra-violet light.
Although the conductive inks which are used have a sufficient electrical conductivity for use in certain circumstances, the electrical conductivity has in no case been as great as the electrical conductivity of copper or other highly conductive metals. Even the conductive inks with the best performance have electrical conductivities which in most cases are only one tenth of the electrical conductivity of copper. It has been proposed to enhance the conductivity of the conductive tracks as continuous printed circuits by electro-plating the tracks with a suitable layer of metal, for example, copper but, in order to carry out electro-plating, it is necessary to have a continuous electrical circuit: that is not conveniently possible where the printed conductive tracks of a printed circuit are discrete and are not connected with one another. Furthermore, electro-plating has required the immersion of the substrate carrying the printed conductive tracks in a bath of suitable electro-plating solution: that technique restricts the substrates which can be subjected to such an immersion electro-plating techniquexe2x80x94for examplexe2x80x94paper based substrates are generally unsuitable as they will tend to be attacked and softened by the electro-plating solution. It has also been proposed to provide a more conductive coating on conductive tracks of printed inks by electroless plating. Electroless plating involves the use of plating solutions which are less stable than those commonly used in electro-plating and the process is less readily controlled. Furthermore, electroless plating still requires the substrate to be immersed in the plating solution with the consequent possibilities of attack of the substrate as well as being restricted in the thickness of deposit.
Thus, it would be advantageous to provide an improved method of providing conductive tracks on a printed circuit by electro-plating. It would be further advantageous to provide an improved printed circuit.
In one aspect the invention relates to a method of providing conductive tracks on a printed circuit including coating a substrate carrying printed tracks with an electro-plating solution with a tool which provides a first electrode of an electro-plating circuit and a second electrode provided by the tracks which are to be electroplated.
In another aspect the invention relates to a tool suitable for use in electro-plating electrically conductive regions of a substrate, the tool including an absorptive member in which plating solution can be carried, a first electrode of an electro-plating circuit adapted to make electrical contact with plating solution carried by the absorptive member, and at least one tool second electrode electrically insulated from the first electrode and spaced from the absorptive member, the tool second electrode being so positioned that as the absorptive member is wiped across a surface of a substrate, the second electrode contactor can be wiped across the surface of the substrate to contact electrically conductive regions of the substrate to form a second electrode of the electro-plating circuit therewith.